abstract class SF::SoundRecorder

• SF::SoundRecorder
• Reference
• Object

Overview

Abstract base class for capturing sound data

SF::SoundBuffer provides a simple interface to access the audio recording capabilities of the computer (the microphone). As an abstract base class, it only cares about capturing sound samples, the task of making something useful with them is left to the derived class. Note that SFML provides a built-in specialization for saving the captured data to a sound buffer (see SF::SoundBufferRecorder).

A derived class has only one virtual function to override:

• on_process_samples provides the new chunks of audio samples while the capture happens

Moreover, two additional virtual functions can be overridden as well if necessary:

• #on_start is called before the capture happens, to perform custom initializations
• #on_stop is called after the capture ends, to perform custom cleanup

A derived class can also control the frequency of the on_process_samples calls, with the #processing_interval= protected function. The default interval is chosen so that recording thread doesn't consume too much CPU, but it can be changed to a smaller value if you need to process the recorded data in real time, for example.

The audio capture feature may not be supported or activated on every platform, thus it is recommended to check its availability with the .available?() function. If it returns false, then any attempt to use an audio recorder will fail.

If you have multiple sound input devices connected to your computer (for example: microphone, external soundcard, webcam mic, ...) you can get a list of all available devices through the available_devices() function. You can then select a device by calling #device=() with the appropriate device. Otherwise the default capturing device will be used.

By default the recording is in 16-bit mono. Using the channel_count= method you can change the number of channels used by the audio capture device to record. Note that you have to decide whether you want to record in mono or stereo before starting the recording.

It is important to note that the audio capture happens in a separate thread, so that it doesn't block the rest of the program. In particular, the on_process_samples virtual function (but not on_start and not on_stop) will be called from this separate thread. It is important to keep this in mind, because you may have to take care of synchronization issues if you share data between threads. Another thing to bear in mind is that you must call #stop() in the destructor of your derived class, so that the recording thread finishes before your object is destroyed.

Usage example:

class CustomRecorder < SF::SoundRecorder
  def finalize
    # Make sure to stop the recording thread
    stop
  end

  def on_start # optional
    # Initialize whatever has to be done before the capture starts
    # [...]

    # Return true to start playing
    true
  end

  def on_process_samples(samples)
    # Do something with the new chunk of samples (store them, send them, ...)
    # [...]

    # Return true to continue playing
    true
  end

  def on_stop # optional
    # Clean up whatever has to be done after the capture ends
    # [...]
  end
end

# Usage
if CustomRecorder.available?
  recorder = CustomRecorder.new

  if !recorder.start
    return -1
  end

  # [...]
  recorder.stop
end

See also: SF::SoundBufferRecorder

Included Modules

• SF::AlResource

Direct Known Subclasses

• SF::SoundBufferRecorder

Defined in:

audio/obj.cr

Class Method Summary

• .available? : Bool

  Check if the system supports audio capture

• .available_devices : Array(String)

  Get a list of the names of all available audio capture devices

• .default_device : String

  Get the name of the default audio capture device

Instance Method Summary

• #channel_count : Int32

  Get the number of channels used by this recorder

• #channel_count=(channel_count : Int)

  Set the channel count of the audio capture device

• #device : String

  Get the name of the current audio capture device

• #device=(name : String) : Bool

  Set the audio capture device

• #finalize

  destructor

• #on_process_samples(samples : Array(Int16) | Slice(Int16)) : Bool

  Process a new chunk of recorded samples

• #on_start : Bool

  Start capturing audio data

• #on_stop

  Stop capturing audio data

• #processing_interval=(interval : Time)

  Set the processing interval

• #sample_rate : Int32

  Get the sample rate

• #start(sample_rate : Int = 44100) : Bool

  Start the capture

• #stop

  Stop the capture

Class Method Detail

Instance Method Detail